Follicular lymphomas is an indolent disease which eventually results in a rapidly proliferating lymphoma. Growth factors which regulate the growth of follicular lymphoma cells are not well described. We have undertaken to identify the autocrine growth factors, if any, which are responsible for follicular lymphoma growth in vitro. We have made the initial observation that follicular lymphoma cells with condition medium, which can be used to support their growth when the cells are plated at low density. In this way we have been able to demonstrate that autocrine factors are produced by these cells. Size fractionation of serum-free conditioned medium reveals that a greater then 10 kd fraction is responsible for the growth promoting activity of unfractioned conditioned medium. Reverse transcription/PCR analysis of follicular lymphoma cell mRNA reveals that these cells produce several interleukins, including IL- 1B, IL-2, GM-CSF and IL-5. IL-1B and IL-2, when added to cells as low density, potentiate their growth to the same degree as conditioned medium, its ability to stimulate cell growth at low density is markedly inhibited. Thus, follicular lymphoma cells appear to possess autocrine growth loops for IL-1B and IL-2.